It's valid for the tiler desc to be 0 when the tiler isn't being
used. Currently, we set the descriptor based on an offset over the
pointer in the gfx state, and if this is 0, we end up setting it to
just the offset when there are more than 8 layers on a target.
Reviewed-by: Lars-Ivar Hesselberg Simonsen <lars-ivar.simonsen@arm.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37837>